FINANCIAL INSTRUMENTS - Cash, Cash Equivalents and Restricted Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash and Cash Equivalents	$ 10,103	$ 6,417
Restricted Investments	199	21,964
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	10,302	28,381	$ 20,873	$ 31,679
SJG
Cash and Cash Equivalents [Line Items]
Cash and Cash Equivalents	1,528	2,678
Restricted Investments	199	4,073
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 1,727	$ 6,751	$ 3,431	$ 3,262